HHH-15663 add @generated(sql=....)

hibernate-core/src/main/java/org/hibernate/annotations/Generated.java

@@ -14,23 +14,35 @@
 import org.hibernate.tuple.GeneratedValueGeneration;
 
 /**
- * Specifies that the value of the annotated property is generated by the database.
- * The generated value will be automatically retrieved using a SQL {@code SELECT}
- * after it is generated.
+ * Specifies that the value of the annotated property is generated by the
+ * database. The generated value will be automatically retrieved using a
+ * SQL {@code select} after it is generated.
  * <p>
- * {@code Generated} relieves the program of the need to call
- * {@link org.hibernate.Session#refresh(Object)} explicitly to synchronize state
- * held in memory with state generated by the database when a SQL {@code INSERT}
- * or {@code UPDATE} is executed.
+ * {@code @Generated} relieves the program of the need to explicitly call
+ * {@link org.hibernate.Session#refresh(Object)} to synchronize state held
+ * in memory with state generated by the database when a SQL {@code insert}
+ * or {@code update} is executed.
  * <p>
- * This is most useful for working with database tables where a column value is
- * populated by a database trigger. A second possible scenario is the use of
- * {@code Generated(INSERT)} with {@link ColumnDefault}.
+ * This is most useful when:
  * <ul>
- *     <li>For identity/autoincrement columns mapped to an identifier property,
- *     use {@link jakarta.persistence.GeneratedValue}.
- *     <li>For columns with a {@code generated always as} clause, prefer the
- *     {@link GeneratedColumn} annotation.
+ * <li>a database table has a column value populated by a database trigger,
+ * <li>a mapped column has a default value defined in DDL, in which case
+ *     {@code Generated(INSERT)} is used in conjunction with
+ *     {@link ColumnDefault},
+ * <li>a {@linkplain #sql() SQL expression} is used to compute the value of
+ *     a mapped column, or
+ * <li>when a custom SQL {@link SQLInsert insert} or {@link SQLUpdate update}
+ *     statement specified by an entity assigns a value to the annotated
+ *     property of the entity, or {@linkplain #writable() transforms} the
+ *     value currently assigned to the annotated property.
+ * </ul>
+ * On the other hand:
+ * <ul>
+ * <li>for identity/autoincrement columns mapped to an identifier property,
+ *     use {@link jakarta.persistence.GeneratedValue}, and
+ * <li>for columns with a {@code generated always as} clause, prefer the
+ *     {@link GeneratedColumn} annotation, so that Hibernate automatically
+ *     generates the correct DDL.
  * </ul>
  *
  * @author Emmanuel Bernard
@@ -44,22 +56,33 @@
 @Retention(RetentionPolicy.RUNTIME)
 public @interface Generated {
 	/**
-	 * Specifies the events that cause the value to be generated by the database.
+	 * Specifies the events that cause the value to be generated by the
+	 * database.
 	 * <ul>
-	 *     <li>If {@link GenerationTime#INSERT}, the generated value will be selected
-	 *     after each SQL {@code INSERT} statement is executed.
-	 *     <li>If {@link GenerationTime#ALWAYS}, the generated value will be selected
-	 *     after each SQL {@code INSERT} or {@code UPDATE} statement is executed.
+	 * <li>If {@link GenerationTime#INSERT}, the generated value will be
+	 *     selected after each SQL {@code insert} statement is executed.
+	 * <li>If {@link GenerationTime#ALWAYS}, the generated value will be
+	 *     selected after each SQL {@code insert} or {@code update}
+	 *     statement is executed.
 	 * </ul>
 	 */
 	GenerationTime value();
 
 	/**
-	 * Determines if the column mapped by the annotated property is included in SQL
-	 * {@code INSERT} and {@code UPDATE} statements. By default, it is excluded.
+	 * A SQL expression used to generate the value of the column mapped by
+	 * the annotated property. The expression is included in generated SQL
+	 * {@code insert} and {@code update} statements.
+	 */
+	String sql() default "";
+
+	/**
+	 * Determines if the value currently assigned to the annotated property
+	 * is included in SQL {@code insert} and {@code update} statements. This
+	 * is useful if the generated value is obtained by transforming the
+	 * assigned property value as it is being written.
 	 *
-	 * @return {@code true} if the mapped column should be included in SQL
-	 *         {@code INSERT} and {@code UPDATE} statements.
+	 * @return {@code true} if the current value should be included in SQL
+	 *         {@code insert} and {@code update} statements.
 	 */
 	boolean writable() default false;
 }

hibernate-core/src/main/java/org/hibernate/annotations/SQLInsert.java

@@ -29,11 +29,17 @@
  * and has no corresponding JDBC parameter in the custom SQL, it must be mapped
  * using {@link jakarta.persistence.Column#insertable insertable=false}.
  * <p>
- * A custom SQL insert statement might transform the column values as they
- * are written. In this case, the state of the entity held in memory loses
- * synchronization with the database after the insert is executed unless
+ * A custom SQL insert statement might assign a value to a mapped column as it
+ * is written. In this case, the corresponding property of the entity remains
+ * unassigned after the insert is executed unless
+ * {@link Generated @Generated(INSERT)} is specified, forcing Hibernate to
+ * reread the state of the entity after each insert.
+ * <p>
+ * Similarly, a custom insert statement might transform a mapped column value
+ * as it is written. In this case, the state of the entity held in memory
+ * loses synchronization with the database after the insert is executed unless
  * {@link Generated @Generated(value=INSERT, writable=true)} is specified,
- * forcing Hibernate to reread the state of the entity after each insert.
+ * again forcing Hibernate to reread the state of the entity after each insert.
  *
  * @author Laszlo Benke
  */

hibernate-core/src/main/java/org/hibernate/annotations/SQLUpdate.java

@@ -32,11 +32,17 @@
  * and has no corresponding JDBC parameter in the custom SQL, it must be mapped
  * using {@link jakarta.persistence.Column#updatable() updatable=false}.
  * <p>
- * A custom SQL update statement might transform the column values as they
- * are written. In this case, the state of the entity held in memory loses
- * synchronization with the database after the update is executed unless
+ * A custom SQL update statement might assign a value to a mapped column as it
+ * is written. In this case, the corresponding property of the entity remains
+ * unassigned after the update is executed unless
+ * {@link Generated @Generated(ALWAYS)} is specified, forcing Hibernate to
+ * reread the state of the entity after each update.
+ * <p>
+ * Similarly, a custom update statement might transform a mapped column value
+ * as it is written. In this case, the state of the entity held in memory
+ * loses synchronization with the database after the update is executed unless
  * {@link Generated @Generated(value=ALWAYS, writable=true)} is specified,
- * forcing Hibernate to reread the state of the entity after each update.
+ * again forcing Hibernate to reread the state of the entity after each update.
  *
  * @author Laszlo Benke
  */

hibernate-core/src/main/java/org/hibernate/cfg/annotations/PropertyBinder.java

@@ -390,7 +390,7 @@ private ValueGeneration determineValueGenerationStrategy(XProperty property) {
 			return NoValueGeneration.INSTANCE;
 		}
 
-		if ( !valueGeneration.writeColumn() ) {
+		if ( !valueGeneration.writePropertyValue() ) {
 			// if we have an in-db generator, mark it as not insertable nor updatable
 			insertable = false;
 			updatable = false;

hibernate-core/src/main/java/org/hibernate/tuple/GeneratedValueGeneration.java

@@ -8,6 +8,8 @@
 
 import org.hibernate.annotations.Generated;
 
+import static org.hibernate.internal.util.StringHelper.isEmpty;
+
 /**
  * A {@link AnnotationValueGeneration} which marks a property as generated in the database.
  *
@@ -18,6 +20,7 @@ public class GeneratedValueGeneration implements AnnotationValueGeneration<Gener
 
 	private GenerationTiming timing;
 	private boolean writable;
+	private String sql;
 
 	public GeneratedValueGeneration() {
 	}
@@ -29,7 +32,8 @@ public GeneratedValueGeneration(GenerationTiming timing) {
 	@Override
 	public void initialize(Generated annotation, Class<?> propertyType) {
 		timing = annotation.value().getEquivalent();
-		writable = annotation.writable();
+		sql = isEmpty( annotation.sql() ) ? null : annotation.sql();
+		writable = annotation.writable() || sql != null;
 	}
 
 	@Override
@@ -50,7 +54,7 @@ public boolean referenceColumnInSql() {
 
 	@Override
 	public String getDatabaseGeneratedReferencedColumnValue() {
-		return null;
+		return sql;
 	}
 }
 

hibernate-core/src/main/java/org/hibernate/tuple/ValueGeneration.java

@@ -9,8 +9,18 @@
 import java.io.Serializable;
 
 /**
- * Describes the generation of values of a certain property of an entity. Property values might
- * be generated in Java, or by the database.
+ * Describes the generation of values of a certain field or property of an entity. A generated
+ * value might be generated in Java, or by the database.
+ * <ul>
+ * <li>Java value generation is the responsibility of an associated {@link ValueGenerator}.
+ *     In this case, the generated value is written to the database just like any other field
+ *     or property value.
+ * <li>A value generated by the database might be generated implicitly, by a trigger, or using
+ *     a {@code default} column value specified in DDL, for example, or it might be generated
+ *     by a SQL expression occurring explicitly in the SQL {@code insert} or {@code update}
+ *     statement. In this case, the generated value is retrieved from the database using a SQL
+ *     {@code select}.
+ * </ul>
  *
  * @see org.hibernate.annotations.ValueGenerationType
  * @see org.hibernate.annotations.Generated
@@ -97,8 +107,10 @@ default boolean generatedByDatabase() {
 	 * <li>{@link #referenceColumnInSql()} is {@code true} and
 	 *     {@link #getDatabaseGeneratedReferencedColumnValue()} returns {@code null}.
 	 * </ul>
+	 *
+	 * @see org.hibernate.annotations.Generated#writable()
 	 */
-	default boolean writeColumn() {
+	default boolean writePropertyValue() {
 		return !generatedByDatabase() // value generated in memory and then written as normal
 			// current value of property of entity instance written completely as normal
 			|| referenceColumnInSql() && getDatabaseGeneratedReferencedColumnValue()==null;